Sealing means for ground reservoirs



April 23, 1968 R. G. JACKSON SEALING MEANS FOR GROUND EESERVOIRS Filed March 24. 1964 Vill in!!! deter Level INVENTOR Roberf Glover JGCkSOII' ATTORNEY United States Patent 3,379,612 SEALING MEANS FOR GROUND RESERVOIRS Robert Glover Jackson, Hornchurch, Essex, England, assignor to Conch International Methane Limited, Nassau, Bahamas, a Bahamian company Filed Mar. 24, 1964, Ser. No. 354,351 Claims priority, application Great Britain, Aug. 19, 1963, 32,7 07/ 63 11 Claims. (G. 61.5)

This invention relates to sealing means for ground reservoirs especially reservoirs for the storage of liquefied gases.

According to British Patent 921,844, and corresponding US. Patent No. 3,175,370, means for sealing a ground reservoir comprises a continuous, vapor-impervious membrane extending down from the roof of the reservoir into a slot in the earth, which slot is filled with a material which is a liquid at ambient temperature but which is solid when the reservoir is in use.

When carrying out the invention of said British Patent 921,844 it has been found that care has to be taken in selecting the material for the slot or gutter so that it does not freeze too soon. If it did freeze too soon, the frozen liquid would impose high stresses on the end of the membrane because the bottom end of the membrane would be locked in position by the frozen material before the rest of the membrane has reached its equilibrium temperature, and hence its equilibrium position with respect to the roof and walls of the reservoir.

In the present modification in and improvement of the invention of British Patent 921,844 a sealing means for a ground reservoir comprises a continuous, fluid-impervious membrane extending down from the roof of the reservoir into a region containing a liquid which freezes below ambient temperature, and a layer of fluid-impermeable, low modulus material secured to at least the inner face of the lower portion of the membrane so that it at least covers that portion of the inner face of the membrane which would otherwise be in contact with said liquid which freezes below ambient temperature. The term low-modulus material in the present specification defines a material having a low modulus of elasticity so that it deforms readily under pressure without rupturing or losing its imperviousness to fluids, and tends to resume its original dimensions when the pressure is removed. It is thus enabled to yield to the expansion and contraction effects of the liquid, when it freezes and melts, without transmitting damaging forces to the membrane which it protects, while maintaining a good seal. In this sealing means any liquid which freezes below ambient temperature can be used.

Ground reservoirs are holes in the surface of the earth, the earth formation surrounding said hole being impervious to the substance being stored. Thus, for example, the earth formation surrounding said hole can contain a liquid which will solidify when the reservoir is charged with the substance to be stored. Alternatively, the hole can be provided with a thick concrete lining to the side walls. A preferred hole in the surface of the earth is a hollow place in the surface of the earth which has a substantial area in the plane of the surface in relation to its capacity, i.e. it is not a narrow shaft or well.

The ground reservoirs are preferably used for storing a liquefied gas, that is a liquid which boils at atmospheric pressure at a temperature below the ambient temperature. The ground reservoirs are especially suitable for storing liquefied gases at atmospheric pressure. Examples of liquefied gases are liquefied natural gas, liquefied methane, and liquefied petroleum gases such as liquefied ethane, or liquefied propane.

The fluid-impervious membrane, that is a material which itself is of insufiicient strength to support loads to which it is subjected is preferably made of metal. When the reservoir is used for storage of liquefied gases, the membrane should be made of a material (e.g. a metal) which does not become embrittled at the low temperatures of the liquefied gas. Examples of such metals and ones which are suitable for reservoirs for the storage of liquefied methane are high nickel steels, stainless steels, copper aluminum or aluminum alloys.

Preferably this membrane is corrugated for flexibility, and especially corrugated horizontally in that part above the low modulus material. It may also if desired be corrugated vertically in that part in contact with the low modulus material. Also, the whole or part of the membrane may be formed out of dimpled metal sheet, again for flexibility. The membrane is eventually sealed at its lower end by means of the liquid which freezes below ambient temperature.

If desired one can use two continuous vapor-impervious membranes extending from the roof to the earth in spaced apart relationship to define a closed space between the outer part of the roof and the ground, which space can be kept full of an inert gas, such as nitrogen or carbon dioxide. The inner membrane is the one described above. The outer membrane need not penetrate into the earths surface provided a fairly gas-tight seal is made with the ground. The outer membrane, if used, may be of metal, wood, rubber or canvas. It may also extend into a region containing a liquid which freezes below ambient temperature but, since it is more remote from the cold of the reservoir when used for storing liquefied gas, it will not generally require a special sealing liquid. Depending on its distance from the reservoir, materials such as water or bitumen may be used.

The roof over the reservoir may be made of any suitable material such as steel, particularly carbon steel, aluminum or wood. In the case of wood, it should be suitably sealed at the joints. The roof must be thermally insulated to prevent as far as possible transfer of heat from the atmosphere into the reservoir. This insulation may be on top of the roof or beneath it or both. In the case of insulation beneath the roof, it may be fixed in contact with the underside of the roof or it may be suspended a short distance from the underside.

The roof is not supported by the membranes and therefore requires suitable supporting members. It is possible when the ground has to be pre-frozen to use the freezing pipes for this purpose. To allow radial movement of the roof due to contraction, the roof may be allowed to slide on top of metal-lined wooden blocks on top of the sup ports.

When the reservoir is in use for a liquefied gas, the pressure of the gas in the reservoir will tend to lift the roof from its supports and the roof should therefore be held down, for example by tie ends connected to the supports, or by counterweighting the roof, or both. For example, the roof may comprise a flat or cambered sheet lined on at least one surface with thermal insulation, a superstructure from which the sheet is suspended, e.g. by hangers flexible in the horizontal direction, and a counterweight acting on said sheet.

The region containing a liquid which freezes below ambient temperature can comprise a continuous gutter containing said liquid. This gutter is preferably a continuous channel e.g. a circular channel when the membrane is cylindrical, dug into the earth. It may however be a trough having sides of wood or metal.

Alternatively, the reg-ion containing a liquid which freezes below ambient temperature can be liquid pervious material, e.g. a layer of sand or gravel, containing said liquid. The membrane can first extend down to the ground level and the ground can be built up by piling a layer of said or gravel round the bottom of the membrane, after which the liquid is introduced.

The temperature at which the liquid freezes is a function of the temperature of the stored liquid in the reservoir, the distance between the liquid and the reservoir and time. Because the provision of low modulus material prevents excessive stresses being exerted on the membrane water can be used, and is obviously the most suitable liquid. However, if desired other liquids freezing below ambient temperature could be used.

It is possible to use a liquid which is still liquid when the reservoir is in use, for example when the reservoir is used for storing a liquid which boils at atmospheric pressure at a temperature not very much below ambient temperature. However in these cases the liquid may evaporate slightly, and it is preferable if the liquid which freezes below ambient temperature is one which is solid when the reservoir is in use.

The fluid-impermeable low modulus material which is secured to at least the inner face of the lower portion of the membrane should be a predominately closed cell porous material so that it is fluid impermeable. The predominately closed porous material should preferably be a synthetic material, especially a plastic material. The most suitable predominately closed cell porous plastics are thermoplastics such as polystyrene, polypropylene, polyurethane, or especially polyvinyl chloride and polyethylene foams.

The fluid-impermeable material must also have a low modulus of elasticity, that is a modulus of less than 1000 lb./in. at compression, e.g. a modulus of between 80 and 100 lb./in. for polyethylene at 10% compression.

The fluid-impermeable low modulus material may be fixed to the end of the membrane by means of adhesives, for example epoxy resin adhesives, or resorcinol glues. Some adhesives contain solvents which may attack the low modulus material and accordingly care should be taken when choosing a suitable adhesive.

Although it is possible to secure the low modulus, material only to the inner face of the lower portion of the membrane, it is preferable to secure said material to both faces so that they at least cover that portion of the membrane which would otherwise be in contact with the liquid which freezes below ambient temperature. This is because when the membrane contracts inwardly it will leave a gap between the outer face and the frozen liquid. This gap may become filled with water seeping in from outside, in which case some stresses may possibly occur on the unprotected membrane when the reservoir is emptied and the membrane moves outwardly again.

An embodiment of this invention is described with reference to the accompanying drawings in which:

FIG. 1 is a highly schematic showing of a sectional elevation of the reservoir;

FIG. 2 shows an enlarged section of the end of the membrane extending into the gutter; and

FIG. 3 shows a modified form of ground seal.

Referring to FIGS. 1 and 2 of the drawings, the ground 2 is frozen by means of freeze pipes 4. Each pipe 4 is a double pipe with the outer one closed at the bottom, and the inner open at the bottom. The inner and outer pipes are connected to ring mains 6 and 5 respectively, and the refrigerant e.g. cold liquid propane, flows from ring main 6 down the inner pipes and up the annular space between the inner and outer pipes into ring main 5 and back to the refrigeration system. The number of freeze pipes depends on the diameter of the hole 1 and can vary from 18 pipes for a diameter of 20 feet to 30 pipes for a diameter of 100 feet.

After the ground is frozen a hole 1 is dug into the ground and an annular channel 3 of large diameter than the hole is dug outside the hole.

The roof comprises a superstructure 7 supported on piers 8, and a flat aluminum membrane sheet 9. This membrane 9 is suspended from the superstructure 7 by means of hangers 10 flexible in the horizontal direction and having thermal insulation blocks 11. The membrane 9 is lined on its underside with thermal insulation 12 carried on an aluminum grid 13 which is supported from the hangers. counterweight blocks 14 rest on the top of the membrane 9 to counteract any upward thrust on the sheet.

The ends of the membrane 9 extend beyond the insulation and extend vertically downwards into the channel 3. Horizontal corrugations 15 allows for thermal expansions and contractions of the membrane.

Strips of closed cell polyvinyl chloride 16, 16 of modulus of elasticity to lb./in. at 10% compression are glued to the lower ends of the membrane 9 by means of an epoxy resin adhesive, or by any other suitable adhesive. There is sufficient polyvinyl chloride so that when the channel 3 contains water, polyvinyl chloride extends above the water level, as shown in FIG. 2. These strips extend completely around the bottom portion of membrane 9, and cover the lower area of the membrane.

When the reservoir is filled with liquified natural gas, the water 17 in the channel 3 freezes, without excessive strain on the membrane. The frozen water effectively seals the end of the membrane so that it acts as a gas-tight seal.

FIG. 3 shows an alternative form of the invention, in which the seal with the ground is made directly by means of frozen water-saturated soil, preferably without digging a channel. The membrane 9 extends down to ground level, and a banking of sand, soil or gravel is built up at 18, 18 at the bottom of the membrane 9. It is now only necessary to saturate the layer 18, 18 with water, which freezes due to the freezing pipes 4, to provide the necessary seal. The sealing strips 16, 16 act as before in absorbing any strain due to temperature changes. Where a channel is dug, the sand or soil may be thrown into the channel after the bottom edge of the membrane is lowered into the channel.

For the sake of clarity, gas vent, liquid inlets and outlets have been omitted. These preferably pass through the roof, but they could enter the reservoir through the side Walls near the top of the reservoir.

It will be apparent that the embodiments shown are only exemplary and that various modifications can be made in construction and arrangement within the scope of the invention as defined in the appended claims.

I claim:

1. A sealing means for a ground reservoir for storing substances below ambient temperature, said reservoir having a fluid-impervious roof above the highest level of the reservoir, which comprises a continuous, fluid-impervious membrane extending down from the roof of the reservoir into a region containing a liquid which freezes at the temperature of the stored substance, and a layer of fluidimpermeable, low modulus material adherently secured to at least the inner face of the lower portion of the membrane so that it at least covers that portion of the inner face of the membrane which would otherwise be in contact with said liquid which freezes at the temperature of the stored substance, said layer being thicker than the membrane and being compressibly deformable to reduce stresses transmitted between the frozen liquid and the membrane.

2. Sealing means as claimed in claim 1, wherein the membrane is made of a thin sheet metal which is relatively unaffected by low temperature.

3. Sealing means as claimed in claim 2 wherein the roof comprises a vapor-impervious sheet lined on at least one surface with thermal insulation, a superstructure from vhich the sheet is suspended, and a counterweight acting on said sheet, said membrance being sealed to the edge of said sheet in fluid-tight relation.

4. Sealing means as claimed in claim 1 wherein the low modulus material is a synthetic plastic material.

5. Sealing means as claimed in claim 4 wherein the plastic is a thermoplastic.

6. Sealing means as claimed in claim 5 wherein the thermoplastic is a plastic foam.

7. Sealing means as claimed in claim 6 wherein the thermoplastic is a polyethylene foam having a modulus of elasticity of between 80 and 100 lb./in.

8. Sealing means as claimed in claim 1 wherein the region containing a liquid which freezes below ambient temperature is a continuous gutter containing said liquid.

9. Sealing means as claimed in claim 1 wherein the region containing a liquid which freezes below ambient temperature is a liquid pervious material containing said liquid.

10-. Sealing means as claimed in claim 1 wherein the liquid which freezes below ambient temperature is water.

11. Sealing means as claimed in claim 1 wherein the low modulus material is secured to :both faces of the membrane so that said material at least covers that portion of the membrane which would otherwise be in contact with the liquid which freezes below ambient temperature.

References Cited UNITED STATES PATENTS 1,151,184 8/1915 Hurlbrink. 2,478,731 8/1949 Wiggins 48178 2,924,350 2/1960 Greer 220-18 X 3,047,184 7/1962 Van Bergen et al. 220-9 3,085,708 4/1963 Dosker 220-9 3,096,902 8/1963 Schroeder 22018 3,195,310 8/1965 Schroeder 61.5 3,205,665 9/1965 Van Horn 61.5

FOREIGN PATENTS 921,844 3/1963 Great Britain.

EARL J. WITMER, Primary Examiner. 

1. A SEALING MEANS FOR A GROUND RESERVIOR FOR STORING SUBSTANCES BELOW AMBIENT TEMPERATURE, SAID RESERVOIR HAVING A FLUID-IMPERVIOUS ROOD ABOVE THE HIGHEST LEVEL OF THE RESERVOIR, WHICH COMPRISES A CONTINUOUS, FLUID-IMPERVIOUS MEMBRANE EXTENDING DOWN FROM THE ROOF OF THE RESERVIOR INTO A REGION CONTAINING A LIQUID WHICH FREEZES AT THE TEMPERATURE OF THE STORED SUBSTANCE, AND A LAYER OF FLUIDIMPERMEABLE, LOW MODULUS MATERIAL ADHERENTLY SECURED TO AT LEAST THE INNER FACE OF THE LOWER PORTION OF THE MEMBRANE SO THAT IS AT LEAST COVERS THAT PORTION OF THE INNER FACE OF THE MEMBRANE WHICH WOULD OTHERWISE BE IN CONTACT WITH SAID LIQUID WHICH FREEZES AT THE TEMPERATURE OF 